Radiation therapy has been employed to treat tumorous tissue. In radiation therapy, a high energy beam is applied from an external source towards the patient. The external source, which may be rotating (as in the case for arc therapy), produces a collimated beam of radiation that is directed into the patient to the target site. The dose and placement of the dose must be accurately controlled to ensure that the tumor receives sufficient radiation, and that damage to the surrounding healthy tissue is minimized.
Generally, a radiation treatment plan is determined before the radiation therapy is performed. Such treatment plan may be determined during a radiation planning session before a treatment session in which treatment radiation is actually delivered to a patient. The goal of the treatment planning is to determine and prescribe a desired dose of radiation to be delivered to a patient.
In radiation therapy, it is important to deliver a desired amount of dose to target, such as a tumor tissue, while minimizing dose to critical organs that contains healthy tissues. Often radiation rays pass through both critical structures and targets during treatment. Intensity modulated radiation therapy (IMRT) uses ray intensities that have been optimized so that homogeneous dose is prescribed to targets while trying to maintain critical organs' dose within acceptable limits. Sometimes if the target moves (for example due to breathing), the intensity rays can be moved according to the target motion to thereby track the target. By tracking the target, the resulting dose in target may have a higher chance of coming out as planned.
However, existing tracking techniques may not provide an accurate tracking of the target. For example, in tracking techniques that predict the position of the target, the actual position of the target may be different from the predicted position. As a result, the delivered beam may not hit the target accurately, and the target may not receive the desired dose as planned.
Also, in some cases, critical organs may not move, or they may move differently from that of the target. In such cases, as the beam is moved to track the target, the resulting intensity rays may move relative to critical organs, and may unintentionally traverse the critical organs, thereby resulting in the critical organs dose that is beyond an acceptable limit. In addition, an inaccuracy of the tracked target position as described above may also cause the critical organs to receive higher dose than planned.